Cosmic Pi - The Recipe

 

Cosmic Pi – The ingredients for our recipe!

A whole batch of Cosmic Pi units

We have a lot of detail about how to assemble a Cosmic Pi unit, how to build the PCB and populate it, and how to program it once assembled. However we don’t really have anywhere that details the complete list of ingredients for all those parts which go together to make the actual detector. So here is the full list, from the outside in:

Case: Hammond 1598JBK (modified reference BASMOD2505), a plastic case with metal front and rear panels. The modifications are for the milling of the front panel to allow connectors to pass through.

Sticker: We laser print AVERY 210X297MM White L4775 sticky labels then cut them (with either a laser, or just scissors depending upon how many lasers we have access to).

Internal fittings and fixings: We use 4 M3 grub screws, 6 M3 nuts and 8 M3 bolts (approx. 6mm length) for all internal fixings (PCB to case, PCB supports, scintillators), and small size wood screws to fix our scintillator supports (approx. 20mm length). We also use two Ettinger 90 degree-mounting brackets to support the Silicon Photo-Multipliers (SiPM) snap-out of the PCB, they are available from Farnell, part number 14.86.313, with 2 being required per Cosmic Pi.

Scintillators: For Cosmic Pi versions 1.6 and 1.7 we use two 10x100x200mm scintillators from Amcrys/ISMA in the Ukraine. The scintillators are pre-drilled, with two 3mm wide by 6mm deep round holes, by the manufacturer that allow for the mounting of the scintillators against the SiPM carrier snap-out. The designation of the scintillator type we use is UPS-923A, which refers to the chemical composition (Amcrys/ISMA product type). If you are unable to obtain this type of scintillator, you should be able to use Saint Gobain BC-408 or other equivalent plastic scintillator material.

Wrapping: The scintillators are individually wrapped in a sheet of aluminium foil (as you probably have in your kitchen!) and sealed up with normal black PVC tape, of the kind used by electricians for electrical isolation. Don’t forget to leave a small hole for the SiPM connection!

Printed Circuit Board (PCB): We have a four layer printed circuit board, the design is available from our github repository (github.com/cosmicpi) along with a full Bill Of Materials (BOM) – for our V 1.6 units and the with some minor changes for our V1.7 units here. The components are generally available electronics, with the exception of the SiPM modules. These are very specialist, high sensitivity photon detectors (sensitive to one or two photons!) which we obtain from Ketek. Each Cosmic Pi unit contains two sensors, of type PM3325-WB. You can find more details and buy the sensors from the ketek website at ketek.net who are based in Germany. The printed circuit board is made from FR4, a typical circuit board material and we apply a lead-free process to all the units we make.

Raspberry Pi: It wouldn’t be a Cosmic Pi without the Raspberry! Each unit has one Raspberry Pi Zero WH single board computer inside the case, complete with a 16 Gb SD card. The Raspberry Pi runs the Wi-Fi interface of the device and the SD card provides all the software that allows you to access and interact with your detector.

Foam, tape and plastic supports: We install some black plastic foam and tape as a light screen within the box, since the scintillators and SiPM are very sensitive to stray light. We also use 3 C shaped plastic supports to hold the scintillator in place.

Do not forget the accessories!

Accessories: In addition to everything inside the box, we also ship with a 9V AC/DC power adapter (the kind of thing that many appliances use for power) and a magnetic GPS antenna module (of the type you would use to add an additional GPS receiver to your car). These plug in to the front of the box in order to make it work.